1. Field of the Invention
The present invention relates to a display device with automatic image correction functionality and, more particularly, to a display device with automatic image correction functionality that does not cause electromagnetic wave interference.
2. Description of the Prior Art
Please refer to the U.S. patent application Ser. No. 09/349088, xe2x80x9cDISPLAY DEVICE WITH AUTOMATIC RESOLUTION CORRECTION FUNCTIONALITYxe2x80x9d, which corresponds to the R.O.C. patent application Ser. No. 87,121,366, and the U.S. patent application Ser. No. 09/597746, xe2x80x9cDISPLAY DEVICE AND METHOD WITH AUTOMATIC IMAGE HORIZONTAL WIDTH CORRECTION FUNCTIONALITYxe2x80x9d, which corresponds to the R.O.C. patent application Ser. No. 88,116,536. Both of these two patent applications teach a display device with automatic image correction functionality, with the former being able to automatically correct the image resolution and the latter being able to automatically correct the horizontal width of the image.
In U.S. patent application Ser. No. 09/349088, xe2x80x9cDISPLAY DEVICE WITH AUTOMATIC RESOLUTION CORRECTION FUNCTIONALITYxe2x80x9d, the display device uses a first counting circuit to count the number of active video horizontal synchronization signals between two vertical synchronization signals, i.e. the number of horizontal lines, and uses a second counting circuit to count the number of sampling timing pulses generated by a phase-locked loop when a video active signal occurs between two horizontal synchronization signals, i.e. the horizontal sampling rate. A control circuit is employed to determine from the number of horizontal lines generated by the first counting circuit a corresponding target sampling rate. The phase-locked loop output is then adjusted until the horizontal sampling rate generated by the second counting circuit approaches or reaches the target sampling rate. This, then, completes the functionality of automatically correcting-displayed images.
In U.S. patent application Ser. No. 09/597746, xe2x80x9cDISPLAY DEVICE AND METHOD WITH AUTOMATIC IMAGE HORIZONTAL WIDTH CORRECTION FUNCTIONALITYxe2x80x9d, the display device uses a first timing circuit to measure the time period between two horizontal synchronization signals, and uses a second timing circuit to measure the time period during which the video signal synchronously transmitted from a computer between the two horizontal synchronization signals is active video. A control circuit is further-employed to compute the longest active video time period among all video signals synchronously received between the two horizontal synchronizing signals according to the time period outputs from the first timing circuit and the second timing circuit. This is then used to correct the horizontal width of the video image displayed on a screen so that the horizontal width of the video image is compatible with that of the screen. The display device further comprises a phase-locked loop for generating a sampling timing pulse to count the first timing circuit and the second timing circuit.
In both the U.S. patent application Ser. No. 09/349088, xe2x80x9cDISPLAY DEVICE WITH AUTOMATIC RESOLUTION CORRECTION FUNCTIONALITYxe2x80x9d and the U.S. patent application Ser. No. 09/597746, xe2x80x9cDISPLAY DEVICE AND METHOD WITH AUTOMATIC IMAGE HORIZONTAL WIDTH CORRECTION FUNCTIONALITYxe2x80x9d, the display devices contain a phase-locked loop to generate the sampling timing pulses needed for counting. The phase-locked loop continuously outputs the sampling timing pulses even when the display device is not performing the automatic image correction functionality, when no sampling timing pulse is needed from the phase-locked loop for counting. These sampling timing pulses are a continuous source of electromagnetic wave interference for other electronic elements in the display device, and affect the normal operation of the display device.
In view of the foregoing, it is a principal objective of the present invention to provide a display device with automatic image correction functionality that is not a source of electromagnetic wave interference. This display device comprises a switch circuit to control the transmission of the sampling timing pulses so that the sampling timing pulses will be output only when the display device is performing the automatic image correction functionality. This greatly reduces the electromagnetic wave interference caused by the sampling timing pulses.
Briefly, the present invention discloses a display device with automatic image correction functionality. The display device has a display screen, a display circuit, an image correction circuit, a timing pulse generator electrically connected to the image correction circuit, and a switch circuit. The switch circuit has a switch electrically positioned between the timing pulse generator and the image correction circuit, and a key electrically connected to the switch for controlling the state of the switch. The switch controls the transmission of the sampling timing pulse from the timing pulse generator to the image correction circuit. When the key is pressed, the switch is activated to permit the sampling timing pulse from the timing pulse generator to transmit to the image correction circuit. The image correction circuit will then perform an automatic image correction to an image frame displayed on the display screen depending on screen frame signals transmitted from a host computer.
It is an advantage of the present invention that the timing pulses from the timing pulse generator are controlled by the switch. Consequently, the pulses are available only when needed to perform the image correction, and so do not continuously interfere with other circuitry within the display device.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in-the various figures and drawings.